build: detect VT_GETMODE on FreeBSD and DragonFly

$ ./waf configure
Checking for vt.h                       : no
Checking for DRM                        : vt.h not found
[...]
 ../test.c:1:10: fatal error: 'sys/vt.h' file not found
 #include <sys/vt.h>
          ^~~~~~~~~~

$ build/mpv --gpu-context=drm /path/to/video.mkv
Error parsing option gpu-context (option parameter could not be parsed)
Setting commandline option --gpu-context=drm failed.

Exiting... (Fatal error)

video/out/drm_common.c

@@ -21,12 +21,19 @@
 #include <sys/ioctl.h>
 #include <poll.h>
 #include <sys/stat.h>
-#include <sys/vt.h>
 #include <unistd.h>
 #include <limits.h>
 #include <math.h>
 #include <time.h>
 
+#include "config.h"
+
+#if HAVE_CONSIO_H
+#include <sys/consio.h>
+#else
+#include <sys/vt.h>
+#endif
+
 #include "drm_common.h"
 
 #include "common/common.h"

wscript

@@ -282,6 +282,12 @@ iconv support use --disable-iconv.",
         'desc': 'vt.h',
         'func': check_statement(['sys/vt.h', 'sys/ioctl.h'],
                                 'int m; ioctl(0, VT_GETMODE, &m)'),
+    }, {
+        'name': 'consio.h',
+        'desc': 'consio.h',
+        'deps': '!vt.h',
+        'func': check_statement(['sys/consio.h', 'sys/ioctl.h'],
+                                'int m; ioctl(0, VT_GETMODE, &m)'),
     }, {
         'name': 'gbm.h',
         'desc': 'gbm.h',
@@ -495,7 +501,7 @@ video_output_features = [
     }, {
         'name': '--drm',
         'desc': 'DRM',
-        'deps': 'vt.h',
+        'deps': 'vt.h || consio.h',
         'func': check_pkg_config('libdrm', '>= 2.4.74'),
     }, {
         'name': '--gbm',